I had it (though for a shorter period of time, as I got pregnant again) - also started with a D&C. In my case - I attribute it to thyroid problems (ended up diagnosed with Hashimoto) and early perimenopause (may also be due to Hashimoto; I did get pregnant twice after, however, once successfully). Not sure which one it was - both hormones were off, and my periods were all over the place too...Might be worthwhile getting a thyroid check and an ultrasound, just in case!